Transposable Prophages in Leptospira: An Ancient, Now Diverse, Group Predominant in Causative Agents of Weil's Disease

The virome associated with the corkscrew shaped bacterium Leptospira, responsible for Weil's disease, is scarcely known, and genetic tools available for these bacteria remain limited. To reduce these two issues, potential transposable prophages were searched in Leptospiraceae genomes. The 236 predicted transposable prophages were particularly abundant in the most pathogenic leptospiral clade, being potentially involved in the acquisition of virulent traits. According to genomic similarities and phylogenies, these prophages are distantly related to known transposable phages and are organized into six groups, one of them encompassing prophages with unusual TA-TA ends. Interestingly, structural and transposition proteins reconstruct different relationships between groups, suggesting ancestral recombinations. Based on the baseplate phylogeny, two large clades emerge, with specific gene-contents and high sequence divergence reflecting their ancient origin. Despite their high divergence, the size and overall genomic organization of all prophages are very conserved, a testimony to the highly constrained nature of their genomes. Finally, similarities between these prophages and the three known non-transposable phages infecting L. biflexa, suggest gene transfer between different Caudovirales inside their leptospiral host, and the possibility to use some of the transposable prophages in that model strain.

Automated summary

By searching for potential transposable prophages in Leptospiraceae genomes, 236 predicted transposable prophages were discovered, especially abundant in the most pathogenic leptospiral clade, potentially involved in acquiring virulent traits. These prophages, distantly related to known transposable phages, are organized into six groups with structural and transposition proteins showing different relationship reconstructions, suggesting ancestral recombinations. Despite high divergence, all prophages exhibit conserved size and genomic organization, with similarities to non-transposable phages infecting L. biflexa, indicating gene transfer between different Caudovirales inside the leptospiral host.